100-7 |
Biochemical changes of threadfin bream during ice storage and their effects on thermal denaturation patterns |
J. YONGSAWATDIGUL, School of Food Technology, Suranaree University of Technology, Nakhon Ratchasima, 30000, Thailand and J. W. Park, OSU Seafood Lab & Dept of Food Sci and Tech, Oregon State University, 2001 Marine Drive #253, Astoria, OR 97103, Albania. Thailand is the largest threadfin bream surimi producer in the world, with production of over 80,000 M/T in 1999. Despite its significant economic value, the knowledge of biochemical changes of threadfin bream muscle proteins, pertinent to surimi quality, is still limited. In addition, thermal denaturation behavior of threadfin bream actomyosin, which directly governs gelation of surimi, has not been well studied. The objectives of this study were to investigate the biochemical and textural changes of threadfin bream kept in ice. In addition, conformational changes during thermal denaturation of actomyosin was elucidated. Threadfin bream(Nemipterus spp.) harvested off the Gulf of Thailand was kept in ice and randomly taken for the following analyses at 0, 3, 6, 9, and 12 days. Nucleotides were separated using reverse-phase HPLC. Total sulfhydryl group was determined by reacting with 5, 5'-dithio-bis-(2-nitrobenzoic acid). Surface hydrophobicity was determined using ANS-fluorecence probe. Ca2+, Mg2+, Mg2+-Ca2+, Mg2+-EGTA, and EDTA-ATPase activity were also measured. Gels of thrice-washed mince were measured using 5 mm spherical probe. For thermal denaturation study, actomyosin extracted from fresh threadfin bream was heated from 10 to 80°C at 1°C/min to measure the dynamic rheological properties using CS50 Bohlin rheometer and a-helix content using spectropolarimeter. A decrease in inosine monophosphate (IMP) was observed within 3 days of ice storage, corresponding to a decrease of Mg2+- and Mg2+-Ca2+-ATPase activities. EDTA-ATPase activity appeared to be constant during the 12-day test period. Ice storage induced conformational changes of actomyosin, as indicated by an increase in total sulfhydryl and surface hydrophobicity on the sixth day. This was in concomitant with a decrease in force at failure. Circular dichroism and storage modulus (G') revealed that unfolding of actomyosin began at 35°C, while aggregation took place at 45°C. This study has elucidated that ice storage (>6 days) of threadfin bream could lead to reduced gel strength due to the conformational changes.
Session 100, Seafood Technology: Texture, Chemistry
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